Engine Car is idling rough and cutting out

Just finished an engine rebuild and the car ran perfect for about 500 miles or so, but now it is intermittently running poorly (doesn't seem mechanically related). Initially, it was idling low and rough and would cut out under load and buck occasionally, and the CEL came on. Then the CEL would turn off and the car would run as if nothing happened. This continued for about 10 minutes until I got home. I dumped codes when I got home, and got 67, 81, 82, and 84. However, before it dumped those codes, the CEL flickered briefly. Not really sure what that means but might be important to include.

I understand that these are EGR codes, I have deleted the EGR system completely and have been running an EGR eliminator plug that I got on LMR a while ago that they no longer sell. It has worked great for the last 3 years.

What could be the issue?

Agreed with the wire connection issue, drove the car today and it had absolutely zero problems, no CEL either. I'll go over the harness.